Abstract

As a powerful optical tool, multiphoton microscopy (MPM) has played an essential role in deep-tissue imaging and in vivo imaging [1]. Among the laser sources for MPM, 1.7 µm laser sources with a low repetition rate have recently become a hot topic for the abilities of 3-photon and 4-photon excitation of most existing fluorescent probes, such as green fluorescent protein and red fluorescent protein [2], which is necessary for high-contrast imaging deep in scattering biological tissues [3]. Although there are few reports on 3-photon microscopy with 1.7-µm laser systems utilizing soliton self-frequency shift [4], which are usually intricate, studies on 1.7-µm low repetition rate fiber lasers are rare. In this work, for the first time, we present a 1.7-µm mode-locked (ML) allfiber laser with a repetition rate of about 1 MHz. It is mode-locked by two semiconductor saturable absorber mirrors (SESAM) and employs a simple and compact linear cavity, opening up broad prospects for multiphoton microscopy at 1.7 µm region.

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